It is widely recognized by vehicle safety authorities that the manually operated restraint belt systems with which most motor vehicles are equipped at the present time are often not used by the vehicle occupants. Many people find it unduly troublesome to do up the belt each time they enter the vehicle and undo it when they leave. They also find the belt somewhat uncomfortable when in restraining position. By the same token, it is also recognized that the safety belts can markedly reduce injuries and fatalities resulting from vehicle accidents.
In order to encourage the use of a safety belt system, a great deal of development effort has gone into the creation of passive type belt systems that are automatically shifted into a restraining configuration when an occupant enters a vehicle and closes the door and automatically transferred to a releasing configuration when the occupant opens the door. Many of these proposed passive systems employ one or more belt guide members that are connected to the restraint belt and are driven back and forth along a guide rail to transfer the engaged portion of the belt between a restraint location and a release location establishing the respective restraint and release configurations of the belt. For example, some types of systems involve a shoulder belt that is connected to a moving anchor that moves along a track located at the edge of the vehicle roof generally above the door. The moving anchor moves between a restraint location above and behind the outboard shoulder of the occupant and a release location at or along the front pillar. In a similar system, the outboard end of a shoulder belt is anchored above and behind the vehicle occupant and passes from the anchor through a movable guide member that moves along a track above the door. Other systems employ a moving anchor or a belt guide member that moves along a guide rail installed on the vehicle door, and there are some systems in which an inboard portion of a lap belt, shoulder belt, or control belt is moved forward and backward.
The drive mechanism for transferring the moving anchor or movable belt guide, which are hereinafter referred to collectively as a belt guide member, often is a reversible, electric motor powered by the vehicle battery and coupled to the belt guide member by a semi-flexible drive element, such as a racked wire, by means of a reduction device. The drive system for the belt guide member should fulfill a number of requirements, and not all drive systems proposed heretofore have met the requirements to the extent necessary to ensure commercial success. Among the requirements is that the device be of compact construction so that it can readily be installed in a small amount of space, such as the space within the vehicle door or within the body of the vehicle adjacent to the door frame. It is also essential that the drive device include a reliable control system to ensure that the belt system remains secured in the restraint location when the occupant is in the vehicle and the door is closed. Any mismatching of the timing or any failure of the device properly to locate the belt guide member at the restraint location can present a great risk to the occupant in the event of an accident. The drive system must also be long-lived and capable of operating reliably through thousands of cycles of operation throughout the useful life of the vehicle. This means that proper lubrication should be provided to minimize wear, and yet the lubrication must not interfere with energy-absorbing devices, electrical systems and the like. Meeting the requirements of reliability and long-life necessitates minimizing shock loads on the components as the drive mechanism is started and stopped, lest repeated shock loads cause wear or breakage to one or more components of the system. This requirement ties in with the requirement for proper timing of the control of the drive system while ensuring that the restraint and release locations of the movable belt guide member are uniformly attained. The foregoing requirements are difficult to achieve in a manner which minimizes manufacturing costs of the system as well as the complexity and expense of assembling the system in the vehicle.